1. Field of the Invention
The present invention relates to a fuel injection control device and an engine control system suitably used for learning a fuel injection characteristic at the time when injection supply of fuel to a target engine is performed.
2. Description of Related Art
As is well known, in an engine (specifically, an internal combustion engine) used as a motive power source of an automobile or the like, fuel injected and supplied with a suitable fuel injection valve (for example, an injector) is ignited and combusted in a combustion chamber in a predetermined cylinder to generate torque in a predetermined output shaft (a crankshaft). In recent years, a diesel engine for the automobile or the like has come to employ a multiple injection method of performing a main injection for generating output torque and also a subsidiary injection of an injection quantity (usually, a minute injection quantity) smaller than that of the main injection before or after the main injection in one combustion cycle. For example, today, inhibition of increase in a noise at the time of the fuel combustion and reduction of a NOx emission quantity are required. In order to respond to the requirements, in some cases, a pilot injection or a pre-injection of a small injection quantity is performed before the main injection. Further, in some cases, an after injection is performed (at timing near the main injection timing during fuel combustion) additionally after the main injection for the purpose of activation of a diffusion combustion, reduction of particulate matter emission and the like. Further, in some cases, a post-injection is performed (at timing largely later than the main injection timing after the end of the fuel combustion) for the purpose of increase of exhaust temperature, activation of a catalyst through supply of a reduction component, and the like. Recent engine control supplies the fuel to the engine in injection modes (injection patterns) suitable for various situations with one or arbitrary combination of the various kinds of the injections.
Generally, an individual difference is caused in the injector during a manufacturing process and the like. Therefore, when the injectors are produced through mass production, injection characteristics of the injectors do not necessarily coincide with each other. Therefore, a no small variation is inevitably caused in the quantity of the actually injected fuel even if the command value of the injection quantity (i.e., an injection period) for the injector is equalized. The injection quantity of the subsidiary injection (specifically, the pilot injection) is smaller than that of the main injection. Therefore, when a difference arises between the desired injection quantity and the actual injection quantity, the difference exerts a large influence. In such the case, there is a possibility that the above described purposes become difficult to achieve even if the difference is small.
Therefore, there has been proposed a device for compensating a characteristic error of the injector including an error resulting from a manufacture variation, aging and the like by sequentially learning the injection characteristic of the injector and by sequentially correcting (calibrating) the error (for example, as described in Patent document 1: JP-A-2005-36788). The device described in Patent document 1 performs a fuel injection (a single-shot injection) of a small injection quantity in a fuel cut period in deceleration of a vehicle. Thus, the device senses a behavior change (in more detail, an increase of rotation speed) of the engine output shaft due to the fuel injection. Also, the device calculates and stores (i.e., learns) the generated torque and eventually the fuel injection quantity based on the sensed rotation speed increase.
There is also a proposed device (as described in Patent document 2: JP-A-2003-254139) as a device that learns the injection characteristic of the injector. In order to control target rotation of the engine output shaft to target rotation speed through feedback control during the engine idling, the device divides a necessary fuel quantity (a required fuel quantity) required for the control of the target rotation into equal quantities (for example, 1 mm3/st each) and performs multiple injections (for example, five steps of injections). The device senses the fuel quantity of the one time of the injection (one injection) among the multiple times of the injections. The device learns the injection characteristic of the injector based on a difference between the sensing value of the fuel quantity (equivalent to the actual injection quantity) and a corresponding reference value. Thus, the injection characteristic of the subsidiary injection (the small quantity injection) can be sensed and stored (i.e., learned) as the injection characteristic of each injection by performing multiple times of the injections during one combustion cycle while securing torque necessary for the idling with the total injection quantity (for example, 5 mm3/st) of the multiple times of the injections.
However, when the inventor conducted the experiment and the like of the device described in each of Patent documents 1 and 2, the inventor acknowledged existence of some shortcomings and found that the device still has a margin for improvement.